1. Field of the Invention
The present invention relates to a fuel supply device configured to supply fuel to an engine, a fuel supply method, and a boat propulsion device including the fuel supply device.
2. Description of the Related Art
Among fuel supply devices that supply fuel to an engine, one type of fuel supply device is equipped with a supply pump, a fuel tank, and a fuel pump, and is well known (see Japan Laid-open Patent Application Publication Nos. JP-A-H10-122077 and JPA-2002-130068). The supply pump is configured to pressurize and feed a liquid fuel to the fuel tank. The fuel tank includes a float, a float valve, and a fuel inflow pipe. The float floats on the liquid surface of the liquid fuel stored in the fuel tank. The float valve is connected to the float and normally closes the opening of the fuel inflow pipe. The float valve is configured to open the fuel inflow pipe when the position of the float becomes lower than a predetermined position. When the opening of the fuel inflow pipe is opened, the liquid fuel pressurized and fed by the supply pump flows into the fuel tank. The fuel pump is configured to suck the liquid fuel stored in the fuel tank. Thus, in the fuel supply device described in Japan Laid-open Patent Application Publication Nos. JP-A-H10-122077 and JP-A-2002-130068, it is required to dispose the supply pump upstream of the fuel tank, and further to dispose the float and the float valve inside the fuel tank.
In view of the above, Japan Laid-open Patent Application Publication No. JP-A-2010-174684 discloses a method of automatically drawing a liquid fuel into a sub fuel tank from a main fuel tank by causing a fuel pump to suck the liquid fuel within the sub fuel tank under the condition that the sub fuel tank is sealed. A fuel supply device described in the Japan Laid-open Patent Application Publication No. JP-A-2010-174684 is not required to be equipped with a supply pump, a float, a float valve and so forth. Thus, the fuel supply device is simply structured.
However, in the fuel supply device described in Japan Laid-open Patent Application Publication No. JP-A-2010-174684, the sub fuel tank may temporarily run out of the liquid fuel when the engine is restarted after a dead soak. This is due to occurrence of the following phenomenon. The fuel within the fuel paths vaporizes due to an increase in temperature of the surroundings of the engine after the dead soak. The pressure in the fuel paths is increased by the vaporized fuel. Accordingly, the fuel, existing in one of the fuel paths that connects the fuel pump and the main fuel tank and is located upstream of the fuel pump, is pushed back to the main fuel tank. When the engine is restarted under this condition, the fuel pump sucks the fuel within the sub fuel tank and supplies the sucked fuel to an injector. When the sub fuel tank then runs out of the fuel, the liquid fuel is drawn into the sub fuel tank due to negative pressure produced when the fuel pump sucks a gas within the sub fuel tank. However, while sucking only the gas, the fuel pump idles. Thus, sufficient negative pressure cannot be produced in the sub fuel tank. Further, an oil-film seal is not provided inside the fuel pump. Thus, the fuel pump cannot sufficiently exert its pump action. As a result, the liquid fuel cannot be quickly drawn into the sub fuel tank.